This invention relates to an apparatus for projecting an original such as a negative film or a positive film, and in particular to a projecting apparatus which enables an original to be read with the imaging magnification thereof varied, in addition to the ordinary reading of the original in a facsimile apparatus, a copying apparatus or the like.
When an original picture such as a microfilm or a 35 mm film is to be read by an image pickup device such as a CCD and an enlarged image of the original picture is to be formed, it has heretofore been possible to obtain the enlarged image by reading the original picture at one-to-one magnification and electrically interpolating the resulting image signal. According to this method, however, the number of picture elements is small and therefore, the image becomes rough and an image of high accuracy cannot be obtained.
In order to overcome such a disadvantage, the applicant has already proposed in Japanese Laid-open Patent Application No. 52819/1985 an apparatus for forming an enlarged image of an original picture by using a projecting apparatus, and then reading the enlarged image by an image pickup device such as a CCD. FIG. 1 of the accompanying drawings shows this proposed reading apparatus.
In FIG. 1, an original picture 1 such as a film illuminated by an illuminating system, not shown, is enlarged and projected by a projection lens 2. A Fresnel lens 3 is disposed on the plane of the image projected by the projection lens 2. The focus of this Fresnel lens 3 is aligned to the position of the exit pupil of the projection lens 2 and therefore, the light having left the Fresnel lens 3 is made parallel to the optic axis of the projection lens 2 and passes through an original supporting glass plate 4. The light passed through the original supporting glass plate 4 is imaged on a solid state image pickup device 6 by an imaging lens 5. The imaging lens 5 and the solid state image pickup device 6 together constitute a head 7, which may be moved in the direction of arrow 8 to read the entire projected image.
In such a reading apparatus, it is desirable that a reproduced image of a desired size of the original be obtained and accordingly, the projection optical system is required to have various imaging magnifications.
It is an object of the present invention to provide a projecting apparatus in which any variation in the imaging magnification of the reproduced image of an original picture does not affect the characteristic of an optical system for reading the reproduced image.
It is a further object of the present invention to provide a projecting apparatus simply mountable on an apparatus capable of reading the optical image from an original on an original supporting table.
To achieve these objects, the projecting apparatus according to the present invention comprises:
means for supporting an original picture; PA1 a projection optical system for forming the image of the original picture; PA1 an optical element disposed on the image side of said projection optical system to cause a principal light ray having entered from the original picture through the projection optical system to travel in parallel to the optic axis of said projection optical system; and PA1 control means for varying the imaging magnification of the original picture by said projection optical system with the spacing between the exit pupil of said projection optical system and said optical element being kept constant.